Plural section magnetically variable inductor with frequency tracked systems



'Jan. 20, 1959 G B CROFTS 2,870,334

PLURAL SECTION MAIGNE'TICALLY VARIABLE INDUCTOR WITH FREQUENCY TRACKEDSYSTEMS Original Filed Jan. 15, 1956 2 Sheets-Sheet l INVENTOR ATTORNEY6'50 965 B. C'POFTS Jan. 20, 1959 G. B. CROFTS 2,870,334

PLURAL SECTION MAGNETICALLY VARIABLE INDUCTOR WITH FREQUENCY TRACKEDSYSTEMS Original Filed Jan. 15, 1956 2 Sheets-Sheet 2 TIIZTE.

m v z m Wafer/0a m6 w WK E E E C 0 v w m A a my 5 GB United States atentPLURAL SECTION MAGNETICALLY VARIABLE ITlEKlIICTOR WITH FREQUENCY TRACKEDSYS- George B. Crofts, La Verne, Calif.

Original application January 13, 1956, Seriat No. 555,973,

now Patent No. 2,786,940, dated March 26, N57. Divided and thisapplication December 6, 1956, Serial No. 626,654

Claims. (Cl. 250-4l) This invention relates to inductance systems andmore especially it relates to systems wherein the inductance of acontrol device is electromagnetically varied by elec tric signals.

Many proposals have been made heretofore to utilize the magneticsaturation of a magnetizable core to control the frequency or impedanceof an associated circuit. While such proposals have found utility tocertain limited extents, they have not been found practicable where aplurality of associated devices or circuits are to be con trolled,either because of the cost of the reactor devices required, or becauseof the difiiculty of magetically segregating the several reactor unitsfrom each other so that undesirable interaction does not occur.

Accordingly, it is one of the principal objects of this invention toprovide a novel system for controlling the impedance or the frequency ofa plurality of separate circuits or devices, by employing a singlemagnetic system having a plurality of discrete saturatable magneticelements which cooperate with the single magnetic system,

but which saturatable elements can be individually controlled byrespective signals without undesirable mutual interaction.

Another object is to provide a variable inductance system employingmeans for setting up a magnetizing field, and an electromagneticsignal-energized device having signal-controlled magnetizing windingswhich are substantially completely enclosed within respectivesaturatable magnetic housings, which can be located in said field,whereby the inductance of said windings can be simultaneously variedwhile completely isolating the magnetic fields of said windings frominteraction with each other and with other devices external thereto.

Another object is to provide an improved signalcontrolled saturatablereactor magnetic transducing system.

A further object is to provide a simple, efiicient and reliable systemfor controlling the impedance or tuning of a plurality of separatecircuits which are required to be magnetically isolated from each other,such for example as the successive tuned stages of a plural-stage radiofrequency amplifier, or the radio frequency amplifier or oscillatorstages of a superheterodyne radio receiver and the like.

A feature of the invention relates to a signal-controlled variableinductance system employing a magnetic circuit in the form of a solenoidwinding, in conjunction with a plurality of discrete saturatablereactors, each comprising its own winding and enclosing magneticcore-housing; all the reactors being located in magnetizablepermeabilitycontrollable relation with said magnetizing circuit, butwithout undesirable mutual coupling between said windings.

A further feature relates to an improved remotely controlled tuningsystem such for example as the tuning stages of a radio receiver,whereby the tuning and frequency tracking of the various elements can beeffected entirely over electric conductors and without requiring anymoving elements such as movable condensers, servomotors and the like.

A still further feature relates to the novel organization, arrangement,and relative location and inter-connection of parts which cooperate toprovide a novel signal-controlled system employing a plurality ofdiscrete saturatable magnetic core devices.

Other features and advantages not specifically enumerated will beapparent after a consideration of the following detailed descriptionsand the appended claims. Accordingly, in the drawing,

Fig. 1 is a sectional view of a signal-controlled plural stage magneticsystem embodying features of the invention;

Fig. 2 is a sectional view of Fig. 1, taken along the line 2-2 thereof;

Fig. 3 shows the invention embodied in a filter;

Fig. 4 shows the invention embodied in connection with a typicalelectron tube oscillator;

Fig. 5 is a modification of Fig. 1;

Fig. 6 shows the modification of Fig. 5 embodied in a superheterodyneradio receiver;

Fig. 7 is a further modification of Fig. 1.

Referring to Figs. 1 and 2 of the drawing, the numeral iii represents asolenoid or magnetizing winding for producing an adjustable steadymagnetic field represented by the arrows 11. Located in serially stackedrelation within the field 11 of the solenoid 10 are a plurality ofsimilar magnetic saturatable reactor devices designated 12, 13. Each ofthe devices 12, 13, for example device 12, may comprise a pair offine-wire coils 14a, 14b, which are wound on a suitable insulating formor bobbin 15. The windings 14a, 14b are completely enclosed within thetwo parts 16, 17 of a bi-part housing of magnetic material. Thatmaterial should be of so-called high frequency iron, for examplecompacted powdered iron such as is conventionally used in iron coreinductances for high frequency transformers and the like.

Both halves 16, 17 of the magnetic housing can be of the sameconstruction, for example of circular shape, each having an annulargroove to receive the winding bobbin 15. The dimensions of the bobbinand the dimensions of the annular grooves are such that the said bi-partsections 16, 17 can be held in close abutting relation to define thecompletely enclosed annular chamber in which the two windings arelocated, thus substantially completely magnetically shielding thewindings enclosed in one pot core from the windings in an adjacent potcore. The two halves 16, 17 can be held in their abutting coaxialrelation by anysuitable means. However, if the center bosses 18, 19 onthe two halves of the housing closely fit the bore 20 of the bobbin,such fastening means may not be required. Similarly the unit 13comprises the two abutting pot core half sections 21, 22, each of highfrequency ferro-magnetic material. In the particular example shown inFig. 1, the winding bobbin 23 may carry only a single winding 24, whichof course is completely housed and enclosed within the two abutting potcore sections 21, 22. The edges of the half sections for he two potcores are provided with notches 25 at suitable points to permit the endsof the respective coils to be brought out for connection to respectiveexternal circuits to be controlled.

The two windings 14a, being in mutual inductive relation may be usedrespectively as the primary and secondary windings of a tuned radiofrequency transformer such for example as the antenna input transformerfor the radio frequency stage of a radio receiver. Either or bothwindings 14a, 14b can be shunted by a of the transformer.

any frequency within the band, the strength of the magnetic field 11 canbe adjusted in any suitable manner, for example by connecting thewinding of solenoid It? to a source, of direct current 27 in series withan adjustable resistor 28, the adjustable arm 29 of which can beprovided with a suitable frequency calibrated scale as shown in Fig. 1.

The strength of the magnetic field represented by the arrows 11determines the degree of magnetic saturation of the pot cores of units12, 13 and hence it determines the permeability of those cores. With apredetermined number. of turns for the windings 14a, 14!), the change inpermeability of their respective pot cores will cause a correspondingsimultaneous variation in the inductance of those windings and hencewill vary the frequency to which both windings are tuned. The tuningband, of course, can be determined either by a fixed shunt capacitanceacross the windings or by their inherent capacitance. Likewise at thesame time that the inductance of windings 14a, 14b is being varied, theinductance of winding 24 is also varied. Winding 24 may constitute thewell known tank inductance for'an electron tube oscillator, such as aHartley oscillator, whose frequency therefore will be varied inaccordance with the calibrated setting of the adjustable arm 29.

It will be understood that the invention is not limited to the provisionof only two pot cores with their respective enclosed windings forcooperation with the common magnetic circuit of coil 10, thus, if areiterative filter is desired, then a number of such pot cores andrespective completely enclosed windings may be used as shownschematically in Fig. 3 wherein the windings 30, 31 are completelyenclosed within their bi-part pot core 32 similar to unit 12 of Fig. 1.The terminals of winding 30 are connected to the input terminals 33, 34of the filter. The terminals of windings 31 can be connected for examplethrough a fixed condenser 35 to the terminals of the single winding 37enclosed within its pot core 36. Similarly the terminals of winding 37can be connected through a fixed condenser 38 to one of the two windings39, 40 which are enclosed within their respective pot cores 41. Theterminals of winding 40 can be connected to output terminals 42, 43 ofthe filter. The common magnetic field similar to the field 11 of Fig. lis represented schematically in Fig. 3 by the dot-dash line 44, and thevariable magnetization of this common magnetic field is representedschematically by the dot-dash arrow.

Referring to Fig. 4 there is shown an arrangement for tuning the wellknown Colpitts oscillator, according to the invention. The parts shownin Fig. 4 which are identical with those in Fig. I bear the samedesignation numerals. Onlya single pot core unit, for example unit 13,is located in the magnetic field. The unit 33 may be connected inparallel with the series-connected tank condensers 45, 46 ofagrid-controlled oscillator tube 47. The junction between the two tankcondensers is connected to cathode 48. The direct current potential forthe anode 49 is supplied by any well known direct current source 50which may be connected in series with a filtering inductance 51, andalso through condenser 52 to one terminal of the tank circuit and of theload circuit represented by resistor 53. The other terminal of the tankcircuit and of the load circuit can be connected to the grid of tube 47.This circuit constitutes the well known Colpitts oscillator whichincludes the condensers 45, 46 and the inductance of unit 13 as the tankcircuit.

The magnetizing current of a magnitude determined by the setting of arm29 and by the potential of source 27, flows through the winding 26 andsets up a magnetic flux through the coil 10. That magnetic flux alsoflows through the completely closed pot core of unit 13 which therebybecomes saturated to an extent determined by the flux density andpermeability of the high frequency iron of which it is constructed.Consequently if the source 27 is a constant voltage source, theresistance 28 can be varied to control the frequency of oscillator 46 bycontrolling the permeability of the pot core of unit 13, which therebycontrols the inductance of the winding of unit 13 constituting the tankinductance of the oscillator.

The invention is particularly advantageous when used in radiotransmission systems employing a series of tuned stages for selectingany particular frequency Within a predetermined reception band, while atthe same time providing means for frequency tracking the stages. Atypical example of such systems is the well known superheterodyne radioreceiver which usually employs a tunable antenna circuit, at least onetunable stage of radio frequency amplification, and a local heterodyneoscillator whose frequency is different from the received carrierfrequency but whose local oscillations must be frequency tracked withthe received carrier for each reception frequency. 7

Such a device is shown in Fig. 5 wherein the parts that are the same asthose of Fig. I bear the same designation numerals. The essentialdifference between the embodiment of Fig. 5 and that of Fig. 1 is thatthe winding of solenoid 10 instead of producing a uniform magnetic fieldfor both units l2, 13, is so designed that the number of turnssurrounding the unit 12 is different from the number of turnssurrounding the unit 13. Thus as shown in Fig. 5, the section of thesolenoid winding around unit 12 has many times the number of magnetizingturns as compared with the number of turns around the unit 713. I havefound that the arrangement of Fig. 5 not only provides a simple way ofvarying the frequency of the respective circuits, but it also provides amore flexible control for effecting a different frequency variation lawfor different pot core units in the magnetic chain.

Fig. 6 shows how the device of Fig. 5 can be embodied in a conventionalsuperheterodyne radio receiver. Thus the unit 12 may have its twowindings 14a, 14b constituting, respectively, the tuned transformercoupling between the antenna and the mixer of the superheterodyne radioreceiver. The winding 24 of unit 13 may constitute the oscillator tankinductance or frequency determining element of the local oscillator 54which also feeds the mixer. in such receivers it may be necessary tohave the antenna and radio frequency coupling inductances tunable overone frequency range with a ratio for example of three to one, whereasthe local oscillator may be tunable over a ratio of two to one. For thatreason the portion of the solenoid winding surrounding unit 12 may havea greater number of turns as compared with the number of turnssurrounding the unit 13. In other words, the turns of the solenoidsurrounding unit 13 may be non-uniformly spaced axially of the solenoidto provide the desired law of frequency variation of the associatedlocal oscillator 54. By this design of the elements it has been foundpossible to provide good tracking of the frequency of the localoscillator 54, of which unit 13 is the frequency determining element,and the antenna and radio frequency circuits to which the windings 14aand 14b are respectively connected.

For example in a superheterodyne radio receiver such as shown in Fig. 6,for use in the standard broadcast band, with the local oscillator 54having a frequency above the received carrier frequency signal, theoscillator winding 24 may have an inductance range of four to one, whilethe antenna and radio frequency amplifier coils 14a, 14b cover a nine toone range.

The embodiment of Fig. 5 lends itself readily to a plug in unit form ofconstruction, in the nature of a tube such as a conventional radio tube.Thus as shown in Fig. 7 the units 12 and 13 which may be similar to thesame units of Figs. 5 or 6, can be stacked and held in stacked array byany suitable means such as adhesive tape or cement. The stacked assemblycan then be attached to any conventional pronged base 55 such as isusually employed in the construction of radio tubes. The variousconnections to the several windings of units 12 and 13 can then be madeto the appropriate prongs or pins 56 carried by the base. If desired,the stacked assembly can be enclosed in a glass or non-magnetic bulb 57which can be cemented to base 55. The magnetizing coil 10 such as shownin Fig. 5 .can then be telescoped over and around the bulb 57 as shownin Fig. 7, and the magnetization of the said coil 10 can be adjusted bymeans of the adjustable resistance 28 and the series connected battery27.

This application is a division of application Serial No. 558,978, filedJanuary 13, 1956 (U. S. Patent No. 2,786,- 940).

Various changes and modifications can be made in the disclosedembodiments without departing from the spirit and scope of theinvention.

What is claimed is:

1. An adjustable inductance device of the kind having a plurality ofsaturatable core reactor units arranged to have their inductance variedsimultaneously by variation of a magnetic field passing therethroughcharacterized in that each unit is provided with at least one highfrequency winding for connection to a corresponding high frequencycircuit, and with each winding substantially completely enclosed withina respective magnetic casing of high frequency iron whereby the windingsof said units are substantially shielded from each other with respect tointeraction between their respective electromagnetic fields, meansincluding a single magnetizing winding surrounding all said units and ofnon-uniform magnetizing power to subject said units to respectivelydifierent steady magnetic field intensities and thereby to track in apredetermined relation the inductance variations of said units over apredetermined frequency band, and means to adjust said steady fieldintensities simultaneously so as to vary simultaneously the inductanceof all said units while preserving said tracked relation.

2. An adjustable inductance device according to claim 1, in which theturns of said magnetizing winding constitute a solenoid having adifferent number of magnetizing turns surrounding one unit as comparedwith the number of magnetizing turns surrounding another unit.

3. An adjustable inductance device according to claim 1, in which theturns of said magnetizing winding are substantially uniformly spacedaxially with respect to one unit but are non-uniformly spaced axiallywith respect to another unit.

4. An adjustable inductance device according to claim 1, in which eachof said units has its winding constituting part of the tuning circuit ofa corresponding high frequency signal transmission system and saidmagnetizing winding is connected to a source of direct current ofadjustable intensity whereby all of said units are tuned simultaneouslyand in said tracked relation by adjustment of said current intensity.

5. An adjustable inductance device according to claim 1, in which eachof said casings is in the form of a bipart cup-like member of compactedhigh frequency powdered iron, said casings having substantially flatopposite faces whereby a series of such casings can be stacked inadjacent serially abutting relation while shielding their respectivewindings from undesirable signal coupling therebetween.

References Cited in the file of this patent UNITED STATES PATENTS1,159,754 Wohlfarth May 23, 1939 2,302,893 Roberts Nov. 24, 19422,503,155 Harvey Apr. 4, 1950 2,581,202 Post Ian. 1, 1952 FOREIGNPATENTS 896,521 Germany Nov. 12, 1953

